HIV-specific neutralizing antibodies (Nabs) have been shown to protect against SHIV infection in the macaque model, suggesting that Nabs of sufficient potency could provide some protection against HIV infection in humans. Given the considerable genetic and antigenic diversity among global circulating strains of HIV, it is critica that protective Nab responses exhibit not only potency for one particular challenge virus, but also cross-subtype breadth and the capacity to neutralize circulating variants that are spreading in high incidence areas. Several Nabs with these characteristics have recently been isolated from HIV-infected individuals. These exciting discoveries demonstrate the capacity of the human immune system to elicit Nabs with broad specificity in response to HIV antigens, and the new Nabs are already being exploited to study passive immune protection. However, these broad antibodies, which were isolated from individuals who had been infected for many years, are the result of extensive somatic hypermutation -- a process that is not possible to mimic with a vaccine immunogen using current technologies. Thus, a critical question is whether broad Nabs that do not require such long-term antigenic stimulation can be elicited at earlier stages in infection. We have identified an individual who has a HIV-specific Nab response with significant cross-subtype breadth at 6 months after HIV infection. We have also identified individuals with exceptionally broad and potent elite neutralizing activity as a result of superinfection. We hypothesize that the Nab responses in these individuals will be distinct from those of singly-infected individuals with longer duration of infection examined in prior studies, including in the extent of somatic hypermutation. Here we propose to characterize the Nab responses in these unique individuals, which will include mapping the NAb specificity and cloning and characterizing the corresponding Nabs. In addition, we will take advantage of banked samples available from these individuals starting before their HIV infection and/or superinfection to examine the evolution of the HIV-specific Nab response -- an approach that has not been possible in any prior studies. We will also continue to screen our cohort for individuals who develop broad Nab responses very early in their infection. These studies are designed to uncover novel pathways to developing broad and potent HIV-specific Nabs. PUBLIC HEALTH RELEVANCE: It is thought that a protective vaccine response to HIV will require broad HIV-specific antibodies. We propose here to isolate and characterize such antibodies from naturally infected individuals. We will also study the process of evolution of such antibody responses, which is important for understanding how to elicit protective HIV antibodies.